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Published year: 20213
Asteroseismic Inference of the Central Structure in a Subgiant Star

Abstract (Expand)

Asteroseismic measurements enable inferences of the underlying stellar structure, such as the density and the speed of sound at various points within the interior of the star. This provides an opportunity … to test stellar evolution theory by assessing whether the predicted structure of a star agrees with the measured structure. Thus far, this kind of inverse analysis has only been applied to the Sun and three solar-like main-sequence stars. Here we extend the technique to stars on the subgiant branch, and apply it to one of the best-characterized subgiants of the Kepler mission, HR 7322. The observation of mixed oscillation modes in this star facilitates inferences of the conditions of its inert helium core, nuclear-burning hydrogen shell, and the deeper parts of its radiative envelope. We find that despite significant differences in the mode frequencies, the structure near to the center of this star does not differ significantly from the predicted structure.

Authors: Earl P. Bellinger, Sarbani Basu, Saskia Hekker, Jørgen Christensen-Dalsgaard, Warrick H. Ball

Date Published: 13th Jul 2021

Publication Type: Journal

TOI-257b (HD 19916b): a warm sub-saturn orbiting an evolved F-type star

Abstract (Expand)

We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to … be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the MINERVA-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of MP = 0.138 ± 0.023 MJ (43.9 ± 7.3 M⊕ ), a radius of RP = 0.639 ± 0.013 RJ (7.16 ± 0.15 R⊕ ), bulk density of 0.65+0.12−0.11 (cgs), and period 18.38818+0.00085−0.00084 days . TOI-257b orbits a bright (V = 7.612 mag) somewhat evolved late F-type star with M* = 1.390 ± 0.046 Msun , R* = 1.888 ± 0.033 Rsun , Teff = 6075 ± 90 K , and vsin i = 11.3 ± 0.5 km s-1. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a ∼71 day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars (∼100) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.

Authors: Brett C Addison, Duncan J Wright, Belinda A Nicholson, Bryson Cale, Teo Mocnik, Daniel Huber, Peter Plavchan, Robert A Wittenmyer, Andrew Vanderburg, William J Chaplin, Ashley Chontos, Jake T Clark, Jason D Eastman, Carl Ziegler, Rafael Brahm, Bradley D Carter, Mathieu Clerte, Néstor Espinoza, Jonathan Horner, John Bentley, Andrés Jordán, Stephen R Kane, John F Kielkopf, Emilie Laychock, Matthew W Mengel, Jack Okumura, Keivan G Stassun, Timothy R Bedding, Brendan P Bowler, Andrius Burnelis, Sergi Blanco-Cuaresma, Michaela Collins, Ian Crossfield, Allen B Davis, Dag Evensberget, Alexis Heitzmann, Steve B Howell, Nicholas Law, Andrew W Mann, Stephen C Marsden, Rachel A Matson, James H O’Connor, Avi Shporer, Catherine Stevens, C G Tinney, Christopher Tylor, Songhu Wang, Hui Zhang, Thomas Henning, Diana Kossakowski, George Ricker, Paula Sarkis, Martin Schlecker, Pascal Torres, Roland Vanderspek, David W Latham, Sara Seager, Joshua N Winn, Jon M Jenkins, Ismael Mireles, Pam Rowden, Joshua Pepper, Tansu Daylan, Joshua E Schlieder, Karen A Collins, Kevin I Collins, Thiam-Guan Tan, Warrick H Ball, Sarbani Basu, Derek L Buzasi, Tiago L Campante, Enrico Corsaro, L González-Cuesta, Guy R Davies, Leandro de Almeida, Jose-Dias do Nascimento, Rafael A García, Zhao Guo, Rasmus Handberg, Saskia Hekker, Daniel R Hey, Thomas Kallinger, Steven D Kawaler, Cenk Kayhan, James S. Kuszlewicz, Mikkel N Lund, Alexander Lyttle, Savita Mathur, Andrea Miglio, Benoit Mosser, Martin B Nielsen, Aldo M Serenelli, Victor Silva Aguirre, Nathalie Themeßl

Date Published: 1st Apr 2021

Publication Type: Journal

Asteroseismology of luminous red giants with Kepler – II. Dependence of mass-loss on pulsations and radiation

Abstract (Expand)

Mass-loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled … by pulsation-enhanced dust-driven outflows. Here, we investigate the relationships between mass-loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 13 5000 ASAS-SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and Wide-field Infrared Survey Explorer(WISE) and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass-loss sets in at pulsation periods above ∼60 and ∼100 d, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C' and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass-loss on the red giant branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3 per cent, less than the typical uncertainty on their asteroseismic masses. Thus mass-loss is currently not a limitation of stellar age estimates for galactic archaeology studies.

Authors: Jie Yu, Saskia Hekker, Timothy R Bedding, Dennis Stello, Daniel Huber, Laurent Gizon, Shourya Khanna, Shaolan Bi

Date Published: 1st Mar 2021

Publication Type: Journal

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